To that end the following collection of quotes -- many of which are authored by Doctors of the Church -- will provide you with the support and encouragement you need to stand your ground and fight for purity.

1. "Blessed are the pure in heart, for they shall see God."
-- Matthew 5:8

2. “Holy Purity, the queen of virtues, the angelic virtue, is a jewel so precious that those who possess it become like the angels of God in heaven, even though clothed in mortal flesh.”
-- Saint John Bosco

3. “We must be pure. I do not speak merely of the purity of the senses. We must observe great purity in our will, in our intentions, in all our actions.”
-- Saint Peter Julian Eymard

4. “Those whose hearts are pure are the temples of the Holy Spirit.”
-- Saint Lucy

5. “We must practice modesty, not only in our looks, but also in our whole deportment, and particularly in our dress, our walk, our conversation, and all similar actions.”
-- Saint Alphonsus Liguori

6. “In the realm of evil thoughts none induces to sin as much as do thoughts that concern the pleasure of the flesh.”
-- Saint Thomas Aquinas

7. "In temptations against chastity, the spiritual masters advise us, not so much to contend with the bad thought, as to turn the mind to some spiritual, or, at least, indifferent object. It is useful to combat other bad thoughts face to face, but not thoughts of impurity.”
-- Saint Alphonsus Liguori

9. “More souls go to hell because of sins of the flesh than for any other reason.”
-- Our Lady of Fatima

10. "Filthy talk makes us feel comfortable with filthy action. But the one who knows how to control the tongue is prepared to resist the attacks of lust."
-- Saint Clement of Alexandria

11. “The man of impure speech is a person whose lips are but an opening and a supply pipe which hell uses to vomit its impurities upon the earth.”
-- Saint John Vianney

12. "Either we must speak as we dress, or dress as we speak. Why do we profess one thing and display another? The tongue talks of chastity, but the whole body reveals impurity."
-- Saint Jerome

13. “A pure soul is like a fine pearl. As long as it is hidden in the shell, at the bottom of the sea, no one thinks of admiring it. But if you bring it into the sunshine, this pearl will shine and attract all eyes. Thus the pure soul, which is hidden from the eyes of the world, will one day shine before the Angels in the sunshine of eternity.”
-- Saint John Vianney

14. “The pure soul is a beautiful rose, and the Three Divine Persons descend from Heaven to inhale its fragrance.”
-- Saint John Vianney

15. “Chastity is the lily of virtues, and makes men almost equal to Angels. Everything is beautiful in accordance with its purity. Now the purity of man is chastity, which is called honesty, and the observance of it, honor and also integrity; and its contrary is called corruption; in short, it has this peculiar excellence above the other virtues, that it preserves both soul and body fair and unspotted.”
-- Saint Francis de Sales

16. “Humility is the safeguard of chastity. In the matter of purity, there is no greater danger than not fearing the danger. For my part, when I find a man secure of himself and without fear, I give him up for lost. I am less alarmed for one who is tempted and who resists by avoiding the occasions, than for one who is not tempted and is not careful to avoid occasions. When a person puts himself in an occasion, saying, I shall not fall, it is an almost infallible sign that he will fall, and with great injury to his soul.”
-- Saint Philip Neri

17. “Your good resolutions must not make you proud, but humble and diffident; you carry a large sum of gold about you, take care not to meet any highwaymen. In this life there is nothing certain: we are in a continual warfare, and, therefore, ought to be on our guard day and night. We sail in a tempestuous sea that threatens us on every side, and in a poor leaky vessel: the devil, who aims at nothing less than our destruction, never ceases to increase the storm, to overwhelm us thereby, if he can; hence it was that the Apostle gave this precaution, even to the virtuous: ‘Let him that thinketh he standeth, take heed lest he fall’ (1 Cor. x.12).”
-- Saint Jerome, Epistle to Saint Eustochium

18. “The state of grace is nothing other than purity, and it gives heaven to those who clothe themselves in it. Holiness, therefore, is simply the state of grace purified, illuminated, beautified by the most perfect purity, exempt not only from mortal sin but also from the smallest faults; purity will make saints of you! Everything lies in this!”
-- Saint Peter Julian Eymard

19. “Chastity, or cleanness of heart, holds a glorious and distinguished place among the virtues, because she, alone, enables man to see God; hence Truth itself said, ‘Blessed are the clean of heart, for they shall see God.’”
-- Saint Augustine

20. “There is no remedy so powerful against the heat of concupiscence as the remembrance of our Savior’s Passion. In all my difficulties I never found anything so efficacious as the wounds of Christ: In them I sleep secure; from them I derive new life.”
-- Saint Augustine

21. “God bestows more consideration on the purity of the intention with which our actions are performed than on the actions themselves.”
-- Saint Augustine

22. “He alone loves the Creator perfectly who manifests a pure love for his neighbor.”
-- Saint Bede the Venerable

23. "You carry your snare everywhere and spread your nets in all places. You allege that you never invited others to sin. You did not indeed, by your words, but you have done so by your dress and your deportment.”
-- Saint John Chrysostom

24. "Let your modesty be a sufficient incitement, yea, an exhortation to everyone to be at peace on their merely looking at you."
-- Saint Ignatius of Loyola